[Fix gate]: Cinder policy change handling in tests

Cinder policies are made more granular and now we need
to adjust the patrole tests to handle those changed policies.

This commit introduces a new flag so that we test the old
policies in stable branches and new one in Xena onwards.

Change-Id: I4be60e3e92704f8e55d3acdb0e025078ae5b21f1
diff --git a/patrole_tempest_plugin/config.py b/patrole_tempest_plugin/config.py
index b01cf10..e6d2515 100644
--- a/patrole_tempest_plugin/config.py
+++ b/patrole_tempest_plugin/config.py
@@ -204,7 +204,12 @@
                 default=True,
                 help="""Are the Nova deprecated API policies available in the
 cloud (e.g. os_compute_api:os-networks)? These policies were
-changed in Victoria.""")
+changed in Victoria."""),
+    cfg.BoolOpt('changed_cinder_policies_xena',
+                default=True,
+                help="""Are the Cinder API policies changed in the
+cloud (e.g. 'group:group_types_specs')? These policies were
+changed in Xena.""")
 ]